Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by ultraviolet radiation

The hypothalamic-pituitary-adrenal (HPA) axis maintains basal and stress-related homeostasis in vertebrates. Skin expresses all elements of the HPA axis including corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), ACTH, β-endorphin (β-END) with corresponding receptors, the glucocorticoidogenic pathway, and the glucocorticoid receptor (GR). To test the hypothesis that cutaneous responses to environmental stressors follow the organizational structure of the central response to stress, the activity of the "cutaneous HPA" axis homolog was investigated after exposure to ultraviolet radiation (UVR) wavelengths of UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm) in human skin organ culture and in co-cultured keratinocytes/melanocytes. The level of stimulation of CRH, POMC, MC1R, MC2R, CYP11A1, and CYP11B1 genes was dependent on UV wavelengths and doses, with the highest effects observed for highly energetic UVC and UVB. ELISA and Western assays showed significant production of CRH, POMC, ACTH, and CYP11A1 proteins and of cortisol, with a decrease in GR expression only after UVB and UVC. However, β-END expression was also stimulated by UVA. Immunocytochemistry localized the deposition of the aforesaid antigens predominantly to the epidermis with additional accumulation of CRH, β-END, and ACTH in the dermis. UVR-stimulated CYP11A1 expression was seen in the basal layer of the epidermis and cells of adjacent dermis. Thus, the capacity to activate or change the spatial distribution of the cutaneous HPA axis elements is dependent on highly energetic wavelengths (UVC and UVB), implying a dependence of a local stress response on their noxious activity with overlapping or alternative mechanisms activated by UVA.